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01-1
A/C system, On Board
Diagnostic (OBD)
Function
The A/C control head -E87- receives input
information from various electrical and electronic
components (sensors).
This information is processed by the control head
in accordance with specified values and then
provides corresponding output signals that
control electrical components (actuators).
The control head is controlled by an internal
microprocessor with On Board Diagnostic (OBD)
capability. If faults or open circuits occur on
applicable components, Diagnostic Trouble
Codes (DTC) are stored in DTC memory. Stored
faults are identified using either VAG1551 Scan
Tool (ST) or VAG1552 Scan Tool (ST). Tables
containing all DTCs and corresponding repair
information guide technicians through the OBD
process.
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01-2
Notes:
This Repair Manual describes On Board
Diagnostic (OBD) with VAG1551 Scan Tool
(ST). OBD procedures can also be performed
with VAG1552 Scan Tool (ST) (VAG1552 Scan
Tool is not equipped with a printer).
Scan Tool VAG1551 or 1552 must be used in in
operating mode -1- (Rapid data transfer).
Operating mode -2- (Flash code output) is not
provided for A/C and Heating OBD.
Always check DTC memory and perform
necessary repairs before erasing DTC memory.
DTC output is possible only if ignition is on or
engine is running and engine speed is less than
3000 rpm (if engine speed is higher, output is
possible only for a limited time or is terminated).
If a fault exists for a certain time it is stored as a
static fault.
If a static fault is no longer present after a
certain time, it is stored as a sporadic fault and
the reference "SP" appears on the upper right
of the VAG1551 display/print-out.
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Before replacing a suspected malfunctioning
component, check all related wiring,
connections, harness connectors and Ground
(GND) connections according to the appropriate
wiring diagram.
Output Diagnostic Test Mode (DTM), Basic
Setting, A/C control head identification and
coding functions are also possible.
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01-3
Notes:
A/C system component locations: engine
compartment page 87-96 .
A/C system component locations: passenger
compartment page 87-106 .
If a the display of a newly installed A/C control
head -E87- flashes after switching the ignition
on (for approximately 2 minutes), code the
control head page 01-57 and execute basic
setting page 01-52 .
If a replacement control head is not coded after
installation or if an unrecognized code was
entered, code "00042" (4-cyl. gasoline engine
USA) is stored.
Control of A/C compressor, flap motors and fan
motors etc. is not possible when executing
Output Diagnostic Test Mode (DTM), function
03 and basic setting, function 04. A/C control is
possible in all other functions.
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01-4
Heating and A/C system changes, 1997
On Board Diagnostic changes
New A/C control head -E87- with specific
coding for m.y. 1997, 4-cyl. and 6-cyl. engines.
Notes:
Before performing On Board Diagnostic of A/C
system, ensure A/C control head -E87- is coded
correctly (according to engine application).
A/C control heads beginning with Part No. 8L0
820 043 should only be installed in m.y. 1997
vehicles.
A/C control heads beginning with Part No. 8D0
820 043 must only be installed in vehicles
through m.y. 1996.
CAUTION!
Part numbers are for reference only.
Always check with your Parts Dept. for the
latest information.
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01-5
Notes:
For m.y. 1997, changes that affect monitoring of
the A/C system by A/C control head -E87- were
made.
Monitored components, locations pages 87-
101 and Page 87-113 .
Additional technical data and notes page 01-
1 .
If a replacement A/C control head is not coded
after installation or if an unrecognized code was
entered, code "04142" (Audi A4 -4cyl. -USA) is
stored.
The A/C control head is no longer connected to
terminal 30 (vehicle electronics). The last input
setting (into the A/C control head) is stored
when the ignition is switched off and retained
when the ignition is switched on.
The duration of time when ignition is off is
calculated by the A/C control head. When
ignition is switched on, the previous "standing
time" is calculated by monitoring a time signal
from the instrument cluster. If more than 4
hours pass since ignition was switched off, the
actual measured values of the outside
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temperature sensor are used as instantaneous
outside and engine temperature inputs for A/C
system control. If "standing time" is shorter than
4 hours, the actual measured values of the
outside temperature sensor are suppressed
and system output temperature control is
calculated by the A/C control head. The
"standing time" period is monitored and used
for this calculation. (Heat radiating from the
engine and radiator leads affects the measured
value of the temperature sensor).
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01-6
The following components previously monitored
by OBD and triggered by A/C control head -E87-
are deleted:
Refrigerant low pressure switch -F73-.
Refrigerant high pressure switch -F118- (low
and high pressure switch functions integrated
into A/C pressure switch, -F29-).
Fresh air/recirculating flap two-way valve -
N63-.
The following new components are monitored by
OBD and provide input signals to -E87-:
A/C pressure switch -F129-.
Sender for outlet temperature, center -G191-.
Sender for outlet temperature, floor outlet -
G192-.
The following components monitored by OBD or
triggered by -E87- are revised:
The heater/air conditioner assembly with all
servo motors.
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The fresh air blower and control module.
Following components that provide input signals
to the A/C control head -E87- are revised:
Instrument cluster
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01-7
A/C system changes
Revised heating/air conditioner assembly with
flap motors page 87-174 .
The air flow flap motor now activates the fresh
air/recirculating air flap as well.
The two way valve for the circulating/fresh air
door, the vacuum unit and the vacuum reservoir
are deleted.
A/C refrigerant circuit changes
New service valve connection on low pressure
side.
Service valve connection for high pressure side
installed in high pressure line in plenum panel
(deleted at condenser).
A/C pressure switch -F129- replaces pressure
switches -F73- and -F118-.
New version "Zexel" compressor and high
pressure line (4-cyl. engines only).
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01-8
VAG1551 Scan Tool (ST), connecting;
A/C control head -E87-, checking
version
Battery Voltage OK
Fuse 22 (S22) OK
Ground (GND) connection on engine and
transmission OK
1996 vehicles
- Open rear passenger ashtray in center console and remove cover for
Data Link Connector (DLC).
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01-9
- With ignition switched off, connect VAG1551 Scan Tool (ST) to Data
Link Connector (DLC) with cable VAG1551/3.
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01-10
1997 vehicles
All vehicles
- With ignition switched off, connect VAG1551 (VAG1552) scan tool to
16-pin Data Link Connector (DLC) under dash to left of steering
column, using adapter cable VAG1551/3.
V
.A.G - ON BOARD DIAGNOSTIC HELP
1 - Rapid data transfer
2 - Blink code output
Indicated on display 1)
1)
Operating modes 1 and 2 are displayed alternately
- Switch on printer with -PRINT- button (indicator lamp in switch will light
up).
- Switch on ignition or start engine.
- Switch A/C compressor on (press "AUTO" button).
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01-11
- Press button -1- for operating mode "Rapid data
transfer."
Rapid data transfer HELP
Enter address word XX
Indicated on display
Notes:
If display is blank, check wiring to VAG1551/power supply using
Troubleshooting Procedure No. 1 in "Electrical Wiring Diagrams,
Troubleshooting and Component Locations" Manual.
Address word for A/C Heating Electronics: 08
Additional operating instructions can be obtained by pressing the
HELP button on VAG1551 Scan Tool (ST)
During testing procedures, the button advances the program to the
next step
An incorrect entry can be cancelled with the -C- button
- Press buttons -0- and -8-.
Rapid data transfer Q
08 - A/C Heating Electronics
Indicated on display
- Press -Q- button to confirm input.
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01-12
If one of the following messages is displayed:
Rapid data transfer HELP
Control module does not answer
Indicated on display
or
Rapid data transfer HELP
K wire not switchin
g
to B+
Indicated on display
- Press HELP button to print out list of possible causes.
Rapid data transfer
No si
g
nal from control module
- Check wiring to Data Link Connector (DLC) according to wiring
diagram Electrical Wiring Diagrams, Troubleshooting & Component
Locations binder.
Rapid data transfer
Error in communication link
If this display appears at the beginning of or during the OBD program,
malfunctions have occurred and data transfer is no longer possible
between the VAG1551 Scan Tool (ST) and the A/C control head -E87-.
Electrical Wiring Diagrams, Troubleshooting & Component Locations
binder
- Check wiring to DLC.
Rapid data transfer Q
08 - A/C Heatin
g
Electronics
- After repairing possible causes of the malfunction, press buttons -0-
and -8- to insert "AC/Heating Electronics" address word 08.
- Press -Q- button to confirm input.
Rapid data transfer
Scan Tool sends address word 08
Indicated on display
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01-13
8D0820043D A4-Klimavollautomat DXX
Coding 00062 WSC ZZZZZ
Indicated on display after approx. 5 seconds
Readout example shows US/CDN version, Zexel A/C compressor, 6
cylinder gasoline engine
Coding -E87- and code tables page 01-57 .
8D0 820 043 D: Part Number of A/C control head -E87-
A4: A/C Heating Electronics component designation
DXX: Software version of A/C control head -E87-
Coding: 00062
WSC 06812: Dealership code
8L0 820 043B A4-
A
/C full
y
automatic DXX
Codin
g
XXXXX WSC ZZZZZ
For m.y. 1997 vehicles install only A/C control head -E87- with Part No.
8L0 820 043 up to and including Part No. index letter "C."
8L0 820 043D A4-
A
/C full
y
automatic DXX
Coding XXXXX WSC ZZZZZ
For vehicles beginning m.y. 1998 install only A/C control head -E87- with
Part No. 8L0 820 043 from Part No. index letter "D."
CAUTION!
Part numbers are listed here for reference only. Always check with
your Parts department for the latest information.
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01-14
Part
number
Comments
8D0 820
043 D - G
Regulation is only switched off in
On Board Diagnostic (OBD)
during output diagnostic test
mode and basic setting.
For vehicles with 6 cylinder
engines, must only be combined
with Zexel compressor.
8D0 820
043 after
H
For all vehicles up to m.y. 96.
8L0 820
043 A - C
For all vehicles up to m.y. 97 (lighting
via terminal 58 and 58d)
8L0 820
043 after
D
For all vehicles up to m.y. 98 without
radio navigation system up to VIN
199999 of m.y. 1999 (lighting
indirectly activated via terminal 58s).
8D0 820
043 K or L
Version with only one display (for
vehicles with radio navigation system
up to VIN 199999 of m.y. 1999)
8D0 820
043 after
M
Version with only one display (for
vehicles as of VIN 200000 of m.y.
1999)
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01-15
Notes:
Zexel A/C compressors were installed from
start of production. During m.y. 1996,
Nippondenso type compressors are installed as
a running change. These compressors are not
equipped with A/C speed sensor G111.
The A/C control head is coded to reflect the
compressor type installed (Zexel or
Nippondenso).
Vehicles equipped with Nippondenso (Denso)
compressors must have A/C control head with
Part No. index "H" or higher installed to allow
for correct coding.
Follow coding exactly when replacing an A/C
control head -E87-.
Parts catalog microfiche
A/C control head varies after VIN 200000 of
m.y. 1999 for vehicles with and without radio
navigation system (or a radio with a large
control panel), with and without switch for
heated seats (e.g. index "M", "N", "P" or "Q").
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Parts catalog microfiche
Depending on VAG1551 Scan Tool (ST)
p
rogram card version, 1st and 2nd digit may not
be displayed (readout: e.g. 040 instead of
00040).
Software version of control head is of no
significance for service department.
If a replacement control head is not coded after
installation or if an unrecognized code was
entered, code "00042" (4-cyl. gasoline engine
USA) is stored.
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01-16
Safety precautions
If special testing equipment is required during
road test, note the following:
WARNING!
Special testing equipment must always be
secured on the back seat and must be
operated from there by a 2nd person.
If special testing equipment were to be
operated from the passenger seat, there
could be injuries to the person seated there
in the event of an accident and air bag
deployment.
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